Multiple pathway models of attention deficit hyperactivity disorder (ADHD) Project Summary/Abstract The goal of this grant is to examine brain differences during executive functioning and reward processing among children with attention deficit hyperactivity disorder (ADHD) and between control and ADHD children. We will examine medication naove 8- to 9-year- olds boys with the combined type of ADHD, because research has shown medication, age-related, sex and subtype effects in ADHD in terms of behavioral performance and brain activation. Response inhibition as measured by a go no-go task will be used to index executive functioning because this cognitive process may be the most common deficit in ADHD children. The executive functioning task will be given under immediate and delayed reinforcement conditions because studies have suggested that ADHD children may have a different delay-of-reinforcement gradient. The central goal of this grant is to determine if the underlying brain abnormalities in ADHD children are characterized by a dichotomous or continuous behavioral distribution. If brain abnormalities are characterized by a dichotomous behavioral distribution (i.e. deficit versus no deficit), we expect that a subset ADHD children will have brain abnormalities restricted to the executive functioning circuit (including ventro-lateral prefrontal cortex and dorsal striatum) and a subset of ADHD children will have brain abnormalities restricted to the reward processing circuit (including orbito-frontal cortex and ventral striatum). We further expect that a subset of ADHD children will have a behavioral deficit in both domains and they may have especially pronounced brain abnormalities in both circuits. Although limited behavioral research on the ADHD combined type suggests that approximately equal numbers of children fall into these neuropsychologically-defined categories, it is possible that there is a more continuous behavioral distribution of executive functioning and reward processing ability. In order to test this hypothesis, we will directly compare a dichotomous to a continuous model using multiple regression. If the dichotomous behavioral model does not explain brain abnormalities, but the continuous model does, then we can conclude that the underlying deficit is characterized by a continuous distribution. If both models explain variance, but the continuous model explains significantly more variance than the dichotomous model, then we can conclude that the underlying deficit has both a continuous and dichotomous component. We will also perform exploratory analyses using Dynamic Causal Modeling (DCM) to examine patterns of effective connectivity between regions of interest in these circuits. PUBLIC HEALTH RELEVANCE: Relevance No studies have examined the neural correlates of ADHD subtypes that have been neuropsychologically-defined based on their behavior, so the results of this grant will have implications for the objective diagnosis of subtypes of ADHD children. This grant will potentially lead to further studies that examine the effect of medical intervention on the neural correlates of executive functioning and reward processing in ADHD subtypes.